To report the distribution and availability of the indicators describing the population of childbearing women in Europe and to assess the impact of the difference in the distribution of two of these indicators (age and multiple births) on some outcome indicators.The six PERISTAT indicators of population characteristics were computed using data from a survey of data providers in Europe. For maternal age and multiple births, the impact on health outcome was simulated for the extremes of the distribution using indirect standardised rates.Data availability is good for basic demographic indicators (age, parity, multiple births), but less complete for indicators of social characteristics (education, smoking, country of birth). Further, common definitions are not used for the latter. Simulations of the impact of maternal age on health outcome found that variation in the maternal age distribution may cause trisomy 21 rates to differ by nearly 20% and maternal mortality ratios by nearly 50%.Indicators of basic population characteristics are not collected routinely in every country. The crude distribution of these indicators is essential for international comparisons. Interpretation of comparative data would be improved by collection of health outcomes and service use by maternal characteristics.